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Technical guidelines for genetic conservation and use Lime Tilia spp. EUFORGEN Jan Svejgaard Jensen Forest and Landscape Research Institute, Hørsholm, Denmark These Technical Guidelines are intended to assist those who cherish the valuable lime genepool and its inheritance, through conserving valuable seed sources or use in practical forestry. The focus is on conserving the genetic diversity of the species at the European scale. The recommendations provided in this module should be regarded as a commonly agreed basis to be complemented and further developed in local, national or regional conditions. The Guidelines are based on the available knowledge of the species and on widely accepted methods for the conservation of forest genetic resources. Biology and ecology Limes (Tilia spp.) are tall trees that can live for up to 500 years. Tilia flowers at the end of June until early July, and T. cordata flowers later than T. platyphyllos. Mast years are infrequent. Tilia sets flowers at the age of 30, and up to ten years earlier on solitary trees. In northern Europe, seed regeneration is sparse, which is assumed to be caused by low temperatures. Tilia species are outcrossing, and at least some of the individuals within a population are selfsterile. Seeds can be stored for a maximum of three - five years. The trees favour good, loamy sites, but can also be found on sandy, infertile soils, and are drought resistant. Dormant shoots of T. cordata can Tilia spp. Tilia spp LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp resist winter frost temperatures as low as -34°C. In most places throughout Europe, T. cordata grows in several types of mixed species forest and many insects and fungi are associated with Tilia. Within the common range of the two species, hybrids between T. cordata and T. platyphyllos have been observed. Hybridization and introgression take place rarely. Examples of hybridization include Tilia x euchlora – a hybrid between T. cordata and T. dasystyla, and Tilia x flaccida (between T. platyphyllos and an American species, T. americana). Leaf, flower and fruit morphology are used for identification of the species. T. cordata and T. platyphyllos trees easily reproduce vegetatively through cuttings and root layers, and cuttings can even be propagated from old trees. Somatic embryogenesis has been carried out both for T. platyphyllos and T. cordata. Distribution Threats to genetic diversity The ecological range of the most important lime species in Europe, T. cordata, is very broad. T. cordata shares roughly the same distribution area as Acer platanoides. It is found in most altitudes, and up to 1500 m in the central Alps. In eastern Europe, it is found in pure stands, but normally exists in mixed stands. Three additional species are also present in Europe: Tilia platyphyllos, T. tomentosa and T. dasystyla. The distribution range of T. platyphyllos is quite limited and is commonly found on sites containing T. cordata, and is rare in northern Europe. T. tomentosa and T. dasystyla occur in southeastern Europe and around the Black Sea. Climatic conditions and human impact have reduced the distribution of Tilia in Europe in the past 2000 years. The competitive ability of beech is also considered as a threat. In many lowland areas, Tilia may have disappeared when humans began farming these areas, limiting the species to marginal sites, and in northern Europe they are thought to have disappeared on many sites due to low seed fertility. However, other stands have evidently been established by humans. Inbreeding caused by the extensive fragmentation and destruction of biotopes is expected to have an impact on both T. cordata and T. platyphyllos. Hybridization, introgression and widespread domestication of foreign species and provenances may also impact the existing genepool. p. Tilia spp. Tilia sp pp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia Genetic knowledge Importance and use Investigations of morphological characteristics of T. cordata have revealed little variation between populations (Pigott 1991). General genetic properties have been described by Giertych (in Bialobok 1991), but genetic knowledge is sparse. Reproductive biology and genetic variability have been reported by Fromm (2001). As for Quercus robur and Q. petraea, leaf, flower and fruit morphology can be used for identification of the species. However, no single morphological trait alone can separate the species due to large variation within the populations for each individual trait (Mauer 1995). Owing to their aesthetic and cultural value as domesticated, urban and landscape trees, limes have become increasingly important in Europe in recent decades. The importance of T. cordata in Europe is well illustrated by the common use of its name for geographic localities. Tilia wood is used for carving, and almost all parts of the tree can be used for fodder, ropes or firewood. Bast and honey, which were historically the main products of Tilia, may have been an important factor in the spread of the species and its status as a typical agroforestry tree in the Middle Ages. Lime trees are insect pollinated, and are important for honeybees and honey production, especially in eastern Europe. Tilia spp. are also important for amenity use, shelterbelts and game plantings in the open landscape, in urban areas and recreational forestry. pp. Tilia spp. Tilia a spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeT Guidelines for genetic conservation and use A network of conservation stands is needed to conserve the genetic variation of limes, which have evolved through adaptation to different ecological and environmental conditions. Conservation and breeding programmes in all countries where lime is found is required to ensure the conservation of the genepool. Specific strategies should include: Sampling strategies: Inventories are needed to provide an overview of the status of genetic conservation in each individual country and at the European scale. For practical purposes, provenance regions can be identified on the basis of ecogeographic variation and can be modified to take into account either expected gene flow or general knowledge about genetic variation within the species. Central core regions: Large genetic reserves within the central core regions of distribution are needed for effective gene conservation purposes and should be given high priority, as large genetic variation is expected to be present in the core distribution area. In general, Tilia occurs in mixed species forest and is associated with a number of different plant species. Existing protected areas will only partly serve as genetic conservation areas, as they are not selected at random nor do they cover the core regions of distribution. Marginal regions: In some regions, large gene reserves of Tilia are lacking, and these genetic resources may be extensively fragmented. They may also be subject to pollen contamination from new plantations originating from non-local seed sources. For these situations, in situ conservation may not be effective. In some of the marginal regions the regeneration of Tilia is lacking or inadequate. Ex situ conservation of Tilia genetic resources is therefore recommended in marginal regions. Preferably, these ex situ conservation stands should be established on the basis of reproductive material from within the local regions, in accordance with in situ silvicultural management principles. In situ conservation in marginal regions should include a larger number of populations. Use and management of genetic resources: Breeding, improvement and management of genetic resources of Tilia should be combined with gene conservation to allow evolutionary forces to continue. Combining conservation and use is especially necessary for species of low economic interest (“use it or lose it”). At some locations the lime trees may be eradicated, if costly and extensive precautions are not taken. Alternatively, these resources could be used to promote the establishment of new populations from local seed collections. Tilia spp. Tilia sp LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.Lim Distribution range of Tilia cordata. Distribution range of Tilia platyphyllos. pp. Tilia spp. Tilia meTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp.LimeTilia spp. EUFORGEN These Technical Guidelines were produced by members of the EUFORGEN Noble Hardwoods Network. The objective of the Network is to identify minimum genetic conservation requirements in the long term in Europe, in order to reduce the overall conservation cost and to improve the quality of standards in each country. Citation: Svejgaard Jensen, J. 2003. EUFORGEN Technical Guidelines for genetic conservation and use for lime (Tilia spp.). International Plant Genetic Resources Institute, Rome, Italy. 6 pages. Selected bibliography Bialobok, S. (ed.). 1991. Nasze Drzewa Lesne. Our Forest Trees. Popular Monograph. Vol 15. Limes - Tilia cordata Mill., Tilia platyphyllos Scop. [in Polish]. Arkadia, Poland. Fromm, M. 2001. Reproduction of an entomophileuos tree species in low density – Small leaved linden (Tilia cordata Mill.) as an example - Dissertation [in German]. Niedersachsische Staats- und Universitätsbibliothek Göttingen, Germany. Http://webdoc.sub.gwdg.de/diss/2001/fromm/fromm.pdf Mauer, W. 1995. Isoenzymatiche und morphologische untersuchungen zur Linde [in German]. Pp 234-243 in Genetics and silviculture with special reference to native oak species (W. Mauer, and U. Tabel). Mitteilungen aus der Forstlichen Versuchsanstalt Rheinland Pfalz 34. Pigott, C.D. and J.P. Huntley. 1981. Factors controlling the distribution of Tilia cordata at the northern limits of its geographical range. III Nature and causes of seed sterility. New Phytologist 87:817-839. Drawings: Tilia cordata, Giovanna Bernetti. © IPGRI, 2003. ISBN: 92-9043-608-5 EUFORGEN secretariat c/o IPGRI Via dei Tre Denari, 472/a 00057 Maccarese (Fiumicino) Rome, Italy Tel. (+39)066118251 Fax: (+39)0661979661 [email protected] More information www.euforgen.org